Demod mode WFM(oirt)

[Stephen Arbogast]

What is the mode WFM(oirt)?  Does it have anything to do with NOAA APT sats?

tnx,

Stephen

[Andrea Lawendel]

Not at all. "OIRT" refers to FM broadcasts in the former Eastern block countries such as Russia or Bielorussia, where a number of frequencies remains carrying transmission in the 67-73 MHz band (only a few channels survive in Ukraine). Parameters like tuning step, bandwidth and emphasis are slightly different from the "Western style" of FM, hence a different type of demodulation, especially used by FM DXer.

Andy

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[Stephen Arbogast]

Thank you!    I searched for some info but could not find anything.

[Robin Gape]

Stephen,

it's not obvious, unless one is long in the tooth, but OIRT really refers to OIRT stereo. There's a short paragraph here https://en.wikipedia.org/wiki/FM_broadcast_band#OIRT_bandplan.

For NOAA APT, the demodulation mode is Narrow FM, and set the user mode bandwidth to 80kHz:

(ignore the 102MHz frequency, which is not for a NOAA weather satellite!)

And then:

Set the mode options (… to the right) as Max dev APT 17kHz or 25kHz

It's probably safe to leave Tau set to 530µs.

The WX Satellite signal is an AM subcarrier at 2.4kHz (IIRC) FM modulated at 17 or 25kHz, thus the baroque configuration to receive it. There is far more at the NOAA website.

HTH, 73, Stay Safe,

Robin, G8DQX

[Stephen Arbogast]

Thanks for the info...    

Stephen

[Stephen Arbogast]

I set  all parameters  to   those   suggested by Robin, G8DQX and  received a good picture this eve from  NOAA-19.    Notes:   1. The  pass was  almost  directly over me(83 degrees  elevation),  Durango, Colorado,  USA,  2.  For  some reason the  audio data recorder started  late so I missed the bottom  of the picture.  3.    I am using   a three element   linearly polarized  Yagi  antenna,  no  az, el rotors.  I point  the beam  at the  point of  closest approach so  I get a narrow view.     My  pic......

Stephen

[Stephen Arbogast]

What if I set tau to zero?  See  https://wiki.gnuradio.org/index.php/FM_Demod

[Stephen Arbogast]

See https://www.electronics-notes.com/articles/audio-video/broadcast-audio/vhf-fm-pre-de-emphasis.php